U.S. patent application number 11/628854 was filed with the patent office on 2007-12-27 for oscillator.
Invention is credited to Werner Ruile, Edgar Schmidhammer.
Application Number | 20070296513 11/628854 |
Document ID | / |
Family ID | 35454968 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070296513 |
Kind Code |
A1 |
Ruile; Werner ; et
al. |
December 27, 2007 |
Oscillator
Abstract
The invention pertains to an oscillator with a resonator element
and a control element for adjusting the resonant frequency of the
resonator element to a plurality of different values, wherein the
resonator element consists of at least one resonator. The control
element can be realized as a control layer for controlling the
propagation speed of the acoustic wave in the resonator. The
control element can alternatively be constructed as a switch
element and be used for switching different sub-branches of a
resonator element constructed as a resonator magazine or a
resonator bank. A trimming element, with which fine-tuning of the
oscillator frequency is possible, is preferably also provided.
Inventors: |
Ruile; Werner; (Munich,
DE) ; Schmidhammer; Edgar; (Stein, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
35454968 |
Appl. No.: |
11/628854 |
Filed: |
May 10, 2005 |
PCT Filed: |
May 10, 2005 |
PCT NO: |
PCT/EP05/05055 |
371 Date: |
July 19, 2007 |
Current U.S.
Class: |
331/116R ;
331/108R; 331/117R |
Current CPC
Class: |
H03B 5/32 20130101; H03B
5/1841 20130101; H03B 5/1864 20130101; H03B 5/366 20130101 |
Class at
Publication: |
331/116.00R ;
331/108.00R; 331/117.00R |
International
Class: |
H03B 5/18 20060101
H03B005/18; H03B 5/24 20060101 H03B005/24; H03B 5/30 20060101
H03B005/30; H03B 5/32 20060101 H03B005/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2004 |
DE |
102004028968.1 |
Claims
1. An oscillator comprising: a resonator element comprising at
least one resonator; and a control element for adjusting a resonant
frequency of the resonator element among a plurality of different
values.
2. The oscillator of claim 1, further comprising: an amplifier
element; and a resonant circuit associated with the amplifier
element, the resonator element being in the resonant circuit.
3. The oscillator of claim 2, wherein the resonator element
comprises a resonator bank comprised of resonators; wherein the
resonant circuit comprises sub-branches in parallel; wherein a
resonator is in each sub-branch; and wherein the control element
comprises a selector switch for selecting among the
sub-branches.
4. The oscillator of claim 3, wherein the control element comprises
switches; and wherein the switch is in each sub-branch.
5. The oscillator of claim 3, wherein at least one of the
resonators has a resonant frequency that is tunable.
6. The oscillator of claim 3, wherein each of the resonators has a
resonant frequency that is tunable.
7. The oscillator of claim 3, wherein at least two of the
resonators have different resonant frequencies.
8. The oscillator of claim 4, wherein at least one sub-branch is
switched into the oscillator circuit at a given point in time.
9. The oscillator of claim 1, wherein the at least one resonator
comprises at least one dielectric resonator.
10. The oscillator of claim 1, wherein the at least one resonator
comprises at least one LC resonator or at least one strip-line
resonator.
11. The oscillator of claim 1, wherein the at least one resonator
comprises at least one micromechanical resonator.
12. The oscillator of claim 1, wherein the at least one resonator
element comprises at least one electroacoustic resonator.
13. The oscillator of claim 12, wherein the at least one resonator
comprises at least one piezoelectric layer; and wherein the control
element comprises a control layer that is in contact with the at
least one piezoelectric layer; and wherein, under mechanical
stress, the control layer influences a propagation velocity of an
acoustic wave in the at least one piezoelectric layer.
14. The oscillator of claim 12, wherein the at least one resonator
comprises at least one piezoelectric layer; wherein the control
element comprises a first control layer and a second control layer,
the first and second control layers forming a composite; and
wherein the second control layer comprises an additional
piezoelectric layer for producing mechanical stress in first
control layer in order to influence a propagation velocity of an
acoustic wave in the piezoelectric layer.
15. The oscillator of claim 13, wherein the control layer has a
giant delta effect under stress.
16. The oscillator of claim 13, wherein the mechanical stress is
generated by a control voltage.
17. The oscillator of claim 13, further comprising: an additional
control element for switching between sub-branches of a resonant
circuit comprised of the at least one resonator.
18. The oscillator of claim 12, wherein the at least one resonator
comprises a thin-film resonator operating with bulk acoustic
waves.
19. The oscillator of claim 18, wherein the at least one resonator
comprises a resonator stack comprising component resonators
arranged in a stack.
20. The oscillator of claim 12, wherein the at least one resonator
operates with surface acoustic waves.
21. The oscillator of claim 20, wherein the at least one resonator
comprises transducers that are longitudinally coupled to each other
acoustically and that are arranged in an acoustic track.
22. The oscillator of claim 2, further comprising: a trimming
element in the resonant circuit.
23. The oscillator of claim 22, wherein the trimming element
comprises a trimming capacitor or a trimming inductor.
24. The oscillator of claim 22, wherein the trimming element is in
parallel with the resonator element.
25. The oscillator of claim 22, wherein the trimming element is in
series with the at least one resonator.
Description
[0001] The invention pertains to an oscillator, in particular, an
oscillator with a resonator in its feedback branch.
[0002] Oscillators with an electrical resonator (thick-film or
thin-film resonator), the dielectric or piezoelectric film of which
consists of quartz, are generally known. The quartz oscillators
generate a signal with a frequency that is stable to a large
extent, which lies between 10 kHz and 200 MHz.
[0003] An oscillator in which a thin-film resonator is arranged in
the feedback branch of a transistor is known from the publication,
B. Otis and J. Rabaey, "A 300 .mu.W 1.9-GHz CMOS Oscillator
Utilizing Micromachined Resonators," IEEE 2003, p. 1271. This
oscillator generates an HF (high frequency) signal at 1.9 GHz. This
signal can be employed as the reference frequency of a modulator in
a portable radio set, for example.
[0004] The oscillator oscillates at a frequency that lies between
the resonant frequency and the antiresonant frequency of the
resonator. An adjustment of the oscillator frequency can be
accomplished inside this interval with, for instance, a trimming
capacitor. The difference between the resonant frequency and the
antiresonant frequency, conditional upon the properties of the
piezoelectric film, is ca. 1-3% in relation to the center
frequency. Therefore only a slight adjustment of the oscillator
frequency is possible.
[0005] The use of a digitally controlled capacitor bank in a
feedback branch of a CMOS-based Pierce oscillator is known from the
publication, Qiuting Huang and P. Basedeau, "Design Considerations
for High-Frequency Crystal Oscillators Digitally Trimmable to
Sub-ppm Accuracy," IEEE 1997, p. 408, FIG. 7. The capacitor bank
can be connected in parallel to a quartz resonator.
[0006] Depending on the application, oscillators are also required
for another frequency, for instance, >2 GHz. In individual
cases, the oscillator frequency can be adjusted by, for instance,
adjusting the resonant frequency of a thin-film resonator by means
of an appropriate thickness of the piezoelectric film, for example.
A subsequent matching of the frequency in another component is not
possible, however.
[0007] The problem of the present invention is to specify an
oscillator with high quality, the frequency of which is externally
adjustable independently of design.
[0008] This problem is solved according to the present invention by
an oscillator with the characteristics of Claim 1. Advantageous
configurations of the invention can be deduced from additional
claims.
[0009] The invention specifies an oscillator with a resonator
element that has an adjustable resonant frequency and a control
element for adjusting the resonant frequency of the resonator to
various values. The resonator element consists of at least one
resonator.
[0010] With a control element it is possible, by controlling the
frequency of the resonator element, to achieve a shift of the
oscillator frequency that exceeds the distance from the resonant to
the antiresonant frequency of an individual resonator. A trimming
element, on the other hand, changes the oscillator frequency
without also shifting the frequency of the resonator element. The
control element on its own is therefore not a trimming element
whose electrical values, particularly the impedance parameters such
as capacitance or inductance, are adjustable. In the sense of the
invention, the resonator element on its own represents a trimming
element or a (preferably externally) controllable "trimming
resonator." The invention therefore has the advantage that a highly
precise adjustment of an oscillator frequency in a wide-band
frequency interval is possible with a resonator element and a
control element. The oscillator of the invention is distinguished
by low phase noise.
[0011] The oscillator of the invention is preferably provided for
the generation of oscillations with a frequency of ca. 1 GHz and
up. The oscillator can have any basic circuitry (e.g., Pierce
oscillator, Colpitts oscillator) with at least one amplifier
element. The amplifier element can be a CMOS (complementary metal
oxide semiconductor) operational amplifier or a field-effect
transistor.
[0012] The oscillator has an oscillator circuit that comprises an
amplifier element and a resonant circuit with a resonator element.
The resonant circuit is arranged in a branch that is, for instance,
a feedback branch of the amplifier element. The resonant circuit
can also be arranged between the input of the amplifier element and
ground.
[0013] In principle, the resonator can be a dielectric resonator.
Alternatively, the resonator can be constructed in strip-line
technology. The resonator can also be an LC resonator. The
formation of the resonator as a micromechanical element is also
possible.
[0014] The resonator is preferably an electroacoustic resonator
(i.e., one operating with acoustic waves). The electroacoustic
resonator preferably has a piezoelectric film.
[0015] In one variant of the invention, the resonator can be a
thin-film resonator (FBAR=Thin Film Bulk Acoustic Wave Resonator)
that has at least one piezoelectric film arranged between two
electrodes. The thin-film resonator can be a membrane-type
resonator arranged over a cavity on a substrate. The thin-film
resonator can be a resonator arranged over an acoustic mirror on a
substrate. The thin-film resonator can be a resonator stack with
several acoustically and/or electrically coupled (component)
resonators arranged one on top of the other. The coupled resonators
can be coupled only acoustically, via a coupling layer.
[0016] In another variant, the resonator can be a resonator
operating with surface waves, such as a DMS resonator (DMS=double
mode SAW, SAW=surface acoustic wave) with transducers acoustically
coupled longitudinally, or a one-gate resonator. A SAW resonator
can be formed as a thin film SAW component in which the
piezoelectric film is produced in thin-film technology.
[0017] The desired frequency shift is done by an appropriate
driving of the control element associated with the resonator or
resonator element. The control element is preferably electrically
driven, preferably by a control voltage.
[0018] In a first preferred variant of the invention, the resonator
element is constructed as a resonator magazine or a resonator bank.
The resonator bank comprises several resonators. The different
resonators preferably have differing resonant frequencies.
[0019] The entire broadband, fully tunable frequency interval is
subdivided into different narrow-band subranges (frequency ranges).
This has the advantage that the phase noise can be kept low in a
narrow-band frequency range. Each frequency range is associated
with a resonator of its own.
[0020] A selector switch or switching elements connect (preferably
exactly) one resonator to the amplifier element of the oscillator.
The selector switch or the switching elements represent a control
element. The selector switch can be available as a finished
component that is suited to select between two or more
sub-paths.
[0021] The resonators are preferably arranged in sub-branches of a
resonant circuit connected to one another in parallel. The
sub-branches are switched on by the corresponding control element
in the resonant circuit. One sub-branch is preferably associated
with one switching element or one terminal of a selector switch.
The switching element is preferably connected electrically in
series to the corresponding resonator.
[0022] At a given time, or in a certain frequency range, at least
one resonator--preferably only one resonator--is switched into the
resonant circuit. In case of switching between different
resonators, the resonant frequency of the resonator, and therefore
the oscillator frequency as well, changes stepwise. For fine-tuning
the oscillator inside a frequency range, a trimming element, e.g. a
trimming capacitor or a trimming inductor, is preferably provided.
It is possible to construct a trimming capacitor as a switchable
capacitor bank, preferably digitally controlled. The capacitor bank
can consist, for instance, of CMOS capacitors. The trimming
capacitor can also be realized as a varactor or "switched
capacitor." Additional trimming elements are also possible.
[0023] In case of multiple turned-on resonators that have different
resonant frequencies, multiple signals with different frequencies
can be generated simultaneously in the oscillator.
[0024] The resonator bank can be constructed of separate
resonators. Preferably, however, all resonators are formed on a
common substrate. The resonator bank can be formed as a chip. In
one variant it is possible to form a chip with a switchable
resonator bank. The control element and the resonator element,
i.e., several resonators, are components of the switchable
resonator bank in this case. The chip can comprise additional
components, particularly the components of the oscillator (e.g., an
amplifier element, switching elements, trimming elements for
fine-tuning the oscillator frequency, L, C, R). Alternatively, the
chip with the resonator bank or the switchable resonator bank can
be mounted on a carrier substrate on which the additional
components of the oscillator are arranged. The chip can be
connected to the carrier substrate by means of bonding wires or in
flip-chip technology. The control elements can also be formed as
one chip each or together as a chip.
[0025] The carrier substrate can have several metal layers
connected to one another via vertical electrical connections, and
interposed dielectric layers, with structures of the oscillator
circuit formed in the metal layers (preferably in the hidden metal
layers).
[0026] The switch elements arranged in the component branches can
be available together in one chip and constitute a switch bank. It
is also possible to construct the switch elements independently of
one another. The switch elements can be semiconductor elements or
micromechanical switches (MEMS).
[0027] In a second preferred variant of the invention, the
resonator element arranged in the resonant circuit of the
oscillator is a resonator that is constructed such that its
resonant frequency is adjustable by a physical--optionally,
mechanical or thermal--effect, for example, as a result of a
deformation of the piezoelectric layer induced by pressure or
tension. A combination of different types of effects, e.g.,
mechanical and thermal, is also possible.
[0028] In this case the control element is preferably solidly
connected to the piezoelectric layer of the resonator. The control
element can be realized as, for instance, a control layer for
controlling the propagation velocity of the acoustic wave in the
piezoelectric layer of the resonator. A stepless tuning of the
resonant frequency of the resonator is also possible.
[0029] A control layer can be formed as a composite of a first and
second control layer. The first control layer is in contact with
the piezoelectric layer of the resonator, and serves to modify the
propagation velocity of the acoustic wave in the piezoelectric
layer of the resonator. The second control layer preferably serves
to create mechanical tensions in the first control layer. The
second control layer is preferably formed as a piezoelectric
control layer.
[0030] A trimming element with which an independent (additional)
fine tuning is possible can be provided in the second preferred
variant as well. This embodiment is particularly space-saving in
relation to the footprint of the arrangement.
[0031] The two preferred variants of the invention can be combined
with one another. In particular, the resonator bank can have
several tunable resonators.
[0032] Current-controlled or voltage-controlled switches (e.g.,
GaAs switches) can be provided as switch elements. The switch
elements can be semiconductor switches such as diodes, transistors
(particularly field-effect transistors) or MEMS switches. The
combination of the various above-mentioned structures in one switch
element or selector switch is also possible.
[0033] The invention will be described in detail below on the basis
of embodiments and associated figures. The figures show various
embodiments of the invention on the basis of schematic
representations not drawn to scale. Identical or identically-acting
parts are labeled with identical reference characters. Shown
schematically are:
[0034] FIG. 1, a known Pierce oscillator with a resonator in the
feedback branch of an amplifier;
[0035] FIG. 2A, an oscillator according to the invention with a
tunable resonator as resonator element;
[0036] FIG. 2B, an embodiment of a tunable resonator as a resonator
bank, the resonators of which are each inserted into sub-branches
of a resonant circuit;
[0037] FIG. 2C, an oscillator with an operational amplifier as
amplifier element, a resonator bank and a selector switch;
[0038] FIG. 3A, a resonator according to the invention with a
field-effect transistor as amplifier element, a resonator bank and
switch elements in the sub-branches of the resonant circuit;
[0039] FIG. 3B, a sub-branch of the resonator circuit with several
sub-branches, wherein the sub-branch has a trimming capacitor;
[0040] FIG. 4, the resonance curves of various resonators in a
resonator bank;
[0041] FIG. 5A, an oscillator with a resonator bank that consists
of tunable resonators (without trimming capacitors);
[0042] FIG. 5B, an oscillator with a resonator bank that consists
of tunable resonators, and with trimming capacitors;
[0043] FIG. 6, an oscillator with a tunable resonator filter that
has acoustically-coupled component resonators;
[0044] FIG. 7, an oscillator according to FIG. 3A, in which the
control elements in the sub-branches are voltage-controlled switch
elements;
[0045] FIG. 8, an oscillator according to FIG. 7, in which the
trimming capacitor is a capacitor bank;
[0046] FIG. 9, a tunable thin-film resonator with a control
layer;
[0047] FIG. 10, a tunable thin-film resonator in which the control
element comprises two control layers;
[0048] FIG. 11, a tunable surface wave filter as a resonator
element in which a control layer is provided;
[0049] FIGS. 12 and 13, a tunable surface wave filter as resonator
element, in which two control elements are provided;
[0050] FIG. 14, as a resonator element, a tunable resonator filter
constructed as a DMS filter;
[0051] FIG. 15, an oscillator with a resonator element in the
collector branch of a transistor;
[0052] FIG. 16, an oscillator with a resonator element in the
emitter branch of a transistor; and
[0053] FIGS. 17 and 18, each an oscillator with a resonant circuit
that is connected to ground at the input of the amplifier
element.
[0054] FIG. 1 shows a known oscillator circuit (Pierce oscillator)
with a resonator RE' and an amplifier element VE. Along with
resonator RE', trimming capacitors C.sub.1 and C.sub.2 (e.g.,
varactors) are arranged in the feedback branch of the oscillator.
The adjustment of the oscillator frequency is done with the aid of
varactors C.sub.1 and C.sub.2. U is a control voltage for adjusting
the operating point of the amplifier element (via an amplifier
stage and a resistor). The generated high-frequency signal is
picked off via an output OUT. The DC component of the signal is cut
off via separation capacitor C.sub.3.
[0055] FIG. 2A shows an oscillator according to the second
embodiment of the invention. The resonant circuit in this case is
arranged in the feedback branch of the amplifier element. The
resonator element is arranged in the feedback branch of amplifier
element VE. The resonator element here consists of a tunable
resonator. The difference from FIG. 1 is that resonator element RE
is itself a trimming element with which the resonant frequency can
be adjusted. Capacitors C.sub.1 and C.sub.2, which are connected in
series to one another and in parallel to the resonator element, are
not tunable in this example. In a variant of the invention,
capacitors C.sub.1 and C.sub.2 can also be tunable.
[0056] In this example, a control element not shown here, such as a
control layer connected to resonator element RE, is formed; see the
explanations for FIGS. 9-13.
[0057] FIG. 2B shows that the tunable resonator element RE
according to the first preferred embodiment of the invention can be
replaced by a switchable resonator bank T1. In FIG. 2B, several
sub-branches electrically connected in parallel to one another are
provided in the feedback branch. Resonator element RE is
constructed as a resonator bank T1 with n resonators RE.sub.j, j=1
through n. Resonators RE.sub.j are each connected in series to an
associated switch element S.sub.j. The respective series circuit of
these elements is arranged in a sub-branch.
[0058] Among the multiple sub-branches, precisely one sub-branch,
for instance, is switched into the resonant circuit at a given
point in time.
[0059] A resonator bank T1 can also be available as a compact
component with external contacts. In one variant of the invention,
the resonator element (or its resonators RE.sub.j) is arranged in a
compact component that also has other components such as switch
elements S.sub.j. It is indicated in FIG. 2C that the individual
switch elements S.sub.j can be replaced by a selector switch S. The
selector switch can also be available as a compact component.
Selector switch S can have several switch elements S.sub.j.
[0060] In the example shown in FIG. 2C, amplifier element VE is
constructed as an operational amplifier. The resonant circuit
comprises the selector switch, resonator element RE, as well as a
series circuit of trimming capacitors C.sub.1 and C.sub.2 balanced
relative to ground. Trimming capacitors C.sub.1 and C.sub.2 here
constitute an (additional) trimming element, which is connected in
parallel to resonator element RE.
[0061] FIG. 3A shows a block schematic of an oscillator with a
field-effect transistor as the amplifier element, a resonator bank
T.sub.1 and individual switch elements S.sub.j, which are arranged
in the sub-branches of the resonant circuit. In this case there is
a voltage-controlled amplifier element. Switch elements S.sub.j can
be alternatively be available as current-controlled switching
elements (e.g., diodes).
[0062] Resonators RE.sub.j preferably have resonant frequencies
f.sub.j differing from one another. Preferably only one resonator
is switched into the resonant circuit in a defined frequency range.
Selecting between the frequency ranges is done by means of switch
elements S.sub.j. The switch elements are controlled such that at
least one switch element (preferably only one switch element) is
switched through in this range. With only one conducting switch
element, all other switch elements are open.
[0063] The oscillator frequency can be fine-tuned inside the given
frequency range with the aid of trimming capacitors C.sub.1 and
C.sub.2.
[0064] FIG. 3B shows one sub-branch of a resonant circuit with
several sub-branches. Alongside resonator RE.sub.j and switch
element S.sub.j, the sub-branch has a trimming capacitor C.sub.j.
In this example, trimming capacitor C.sub.j is connected in series
with the respective resonator RE.sub.j.
[0065] FIG. 4 shows the resonance curves of various resonators in a
resonator bank. Resonance curve 1 is associated with first
resonator RE.sub.j. Resonance curves 2 and 3 are associated,
respectively with second and third resonator RE.sub.2 and RE.sub.3.
In switching from the first to the second or third resonator, the
transition between resonance curve 1 to resonance curve 2 or 3
takes place.
[0066] It is indicated in FIG. 5A that resonators RE.sub.j of a
resonator bank T1 can each be tunable. It is also possible for only
one resonator or a part of the resonators to be constructed tunably
in a resonator bank.
[0067] In this case, the fine-tuning of the resonator frequency can
be carried out in the respective tunable resonator. In principle,
therefore, additional trimming elements are not necessary.
[0068] It is indicated in FIG. 5B that additional trimming
capacitors can nevertheless be provided. It is also possible for
resonator RE.sub.j in one sub-branch illustrated in FIG. 3B to be
tunable, as is provided in the second embodiment of the
invention.
[0069] An oscillator with an operational amplifier as amplifier
element VE is shown in FIG. 6. A resonator element RE and matching
networks AN1 and AN2 are arranged in the feedback branch of the
amplifier element. In principle, the matching networks can be
provided in a resonant circuit branch or in its sub-branches. It is
also possible to forgo adapting networks AN1, AN2 in the example of
FIG. 6.
[0070] The resonator element here is provided as a tunable
resonator filter with at least two acoustically coupled component
resonators (e.g., transducers). For instance, the tunable resonator
filter can be constructed as a DMS filter operating with surface
acoustic waves, as in FIG. 14. The resonator filter can be formed
as resonator stack with coupled thin-film resonators.
[0071] The component resonators in this example are also
electrically connected to one another. It is also possible for the
component resonators of a thus-constructed resonator element RE to
be coupled only acoustically to one another. In a resonator stack,
the acoustic coupling can occur through a coupling layer arranged
between two component resonators.
[0072] In the example of FIG. 7, switch elements S.sub.j are formed
as voltage-controlled elements (field-effect transistors). Switch
element S.sub.j is triggered by means of a control voltage
U.sub.j.
[0073] It is indicated in FIG. 8 that the trimming capacitors in
trimming element T2 can be constructed as capacitor banks C'.sub.1
and C'.sub.2. The capacitor banks are controlled, preferably
digitally, via input IN. The capacitor banks are preferably each
connected to ground for balancing. It is also possible, however,
for the capacitors arranged in the capacitor bank not to be
connected to ground.
[0074] A thin-film resonator is shown in cross section in FIG. 9.
The resonator here is produced as a multilayer element on a
substrate SU. It comprises a control layer GDE, above which a
tightly contacting piezoelectric layer PS is formed, which is
furnished on one side with a pair of HF electrodes ES1 for exciting
a volume acoustic wave, and on the other, with a pair of control
voltage electrodes ES2. The control layer is preferably a so-called
GDE (Giant Delta E) layer, i.e., a layer that has a "giant delta E"
effect.
[0075] GDE materials are materials that have an unusually large
change in their modulus of elasticity under mechanical stress. A
number of such materials from many different material classes have
become known in recent times.
[0076] A large change of rigidity due to mechanical stresses is
achieved, for instance, with certain metallic glasses, so-called
met glasses, which mainly consist of the metals iron, nickel and
cobalt. For instance, met glasses with the compositions
Fe.sub.81Si.sub.3.5B.sub.13.5C.sub.2, FeCuNbSiB,
Fe.sub.40Ni.sub.40P.sub.14B.sub.6, Fe.sub.55Co.sub.30B.sub.15 or
Fe.sub.80 with Si and Cr have a large delta E effect. Such met
glasses are known, for instance, under the trade name VITROVAC.RTM.
4040 from vacuum casting or under the designation Metglas.RTM. 2605
SC (FE.sub.81Si.sub.3.5B.sub.13.5C.sub.2).
[0077] In the advantageous embodiment shown in FIG. 9, the top
electrode represents both one of the HF electrodes and one of the
control voltage electrodes at the same time. The second HF
electrode and the second control voltage electrode are arranged on
piezoelectric layer PS on top of the control layer.
[0078] In another embodiment, second HF electrode ES1 can be
arranged underneath piezoelectric layer PS. The second control
voltage electrode of electrode pair ES2 can lie as a thin metallic
film either above or below control layer GDE. The latter
possibility is indicated in FIG. 9 by the optionally provided metal
film ME. Another possibility is that the control layer replaces one
of the HF electrodes or control voltage electrodes. The control
voltage electrodes can continue to be arranged transverse to the
piezoelectric layer.
[0079] The thicknesses of piezoelectric layer PS and control layer
GDE are selected such that both layers lie within the penetration
depth of the acoustic wave.
[0080] The thickness ratio of piezoelectric layer PS to control
layer GDE within the range of the penetration depth is another
adjustable parameter for the invented component. The greater the
proportion of the control layer inside the penetration depth is,
the greater is the tuning range over which the operating frequency
or center frequency of the filter can be shifted. A larger
proportion of piezoelectric layer PS inside the penetration depth,
on the other hand, increases the coupling, and thus the bandwidth,
of the filter. Depending on the desired properties of the
component, the ratio is adjusted such that either a high degree of
coupling or a high tunability is obtained relative to both
properties.
[0081] The acoustically active part of the component can be
separated from substrate SU by an acoustic mirror AS, which assures
a one-hundred percent reflection of the acoustic wave back into the
acoustically active part of the component.
[0082] Another possibility is for the control layer to represent a
sub-layer of acoustic mirror AS. The important point here as well
is that the control layer lie within the penetration range of the
acoustic wave, so that in this embodiment in particular, the
control layer is an upper sub-layer of the acoustic mirror. Thus a
better tunability is achieved via the control layer.
[0083] It is also possible for the lower control or HF electrode to
represent a sub-layer of acoustic mirror AS.
[0084] The varying voltage applied to the control electrodes is
used for frequency tuning of the filter. In the above-mentioned
embodiment from FIG. 9, piezoelectric layer PS takes on a double
function as an excitation layer for exciting volume acoustic waves
and as a tunable layer for generating a mechanical stress, which is
transferred to the control layer and elicits a change in material
rigidity. The latter in turn influences the propagation velocity of
the acoustic wave and thus the center frequency of the filter.
[0085] FIG. 10 shows the cross section of another advantageous
embodiment of a tunable thin-film resonator. Piezoelectric
excitation layer PS1 lies between two HF electrodes ES1. The lower
of these electrodes ES1 simultaneously represents a control voltage
electrode ES2. Underneath it, a first control layer GDE is
arranged, which in another possible embodiment can replace the
latter-mentioned electrode if first control layer GDE is
electrically conductive. Between layer GDE and the lower of the
control voltage electrodes ES2 lies a second control layer PS2 (the
piezoelectric tuning layer).
[0086] A tunable resonator operating with surface waves is shown in
FIG. 11 in a schematic cross section.
[0087] The resonator comprises a control layer GDE, above which a
tightly contacting piezoelectric layer PS is formed. Electrode
structures ES1 are formed on the surface of piezoelectric layer PS.
The acoustic waves generated by electrode structures ES1, such as
interdigital transducers, have a penetration depth of roughly
one-half wavelength into the multilayer structure. The thicknesses
of piezoelectric layer PS and control layer GDE are selected such
that both layers lie within the penetration range of the acoustic
wave.
[0088] A first control voltage electrode ES2 is arranged on the
upper side of piezoelectric layer PS, which carries acoustic
structures such as interdigital transducers and reflectors.
Electrically conductive control layer GDE serves as second control
electrode ES2 in this embodiment.
[0089] In addition, the second control electrode can be arranged
above or below control layer GDE.
[0090] In the embodiment shown in FIG. 11, piezoelectric layer PS
serves both to excite surface acoustic waves and to control the
electrical properties of underlying control layer GDE by means of
mechanical stresses that appear as a result of the inverse
piezoelectric effect when a varying control voltage is applied.
[0091] FIG. 12 shows, on the basis of a schematic cross section, an
additional example of a resonator operating with surface acoustic
waves, wherein first control layer GDE is arranged between
piezoelectric excitation layer PS1 and piezoelectric tuning layer
PS2 (second control layer). A control voltage electrode ES2 lies
underneath tuning layer PS2. Second control electrode ES2 can be
formed either as first control layer GDE or as an additional metal
layer above or below first control layer GDE.
[0092] A tunable surface wave filter without a carrier substrate is
shown in FIG. 13. The acoustic structures, such as interdigital
transducers or reflectors, are situated on the upper side of
piezoelectric excitation layer PS1. First control layer GDE is
arranged between excitation layer PS1 and second control layer PS2.
The latter is furnished on both sides with control voltage
electrodes ES2.
[0093] An additional variation possibility is to form upper control
voltage electrode ES2 as the first control layer.
[0094] FIG. 14 schematically shows the structure of a (tunable) DMS
filter. Two transducers W1, W2 are arranged here side-by-side in an
acoustic track and are acoustically coupled to one another.
Transducers W1, W2 are arranged between two reflector structures. A
first transducer W1 is connected to a first signal terminal RF1. A
second transducer W2 is connected to a second signal terminal RF2
of the resonator filter. Both transducers are connected to
ground.
[0095] A control layer, not shown in FIG. 14, can be designed
according to the arrangements shown in FIGS. 11-13.
[0096] Additional possible configurations of an oscillator
according to the invention are shown in FIGS. 15-18. Resonator
element RE in FIG. 15 is arranged in the collector branch of a
transistor. In FIG. 16, resonator element RE is arranged in the
emitter path of a transistor. Resonator element RE in FIGS. 17 and
18 is connected to ground at the input of the amplifier
element.
[0097] In FIG. 16, R.sub.L stands for a load resistor. Resonator
element RE is connected in parallel with an inductor L.sub.P.
Additional trimming elements (a trimming inductor and a trimming
capacitor) other than tunable resonator element RE are also
provided.
[0098] This invention is not limited to the embodiments, oscillator
types (e.g., Pierce, Colpitts, Clapp oscillators) or number of
illustrated elements presented above. The resonators (e.g., SAW,
FBAR) can be temperature-compensated to increase frequency
stability.
List of Reference Characters
[0099] RE Resonator element [0100] RE.sub.1 . . . RE.sub.n
Resonator [0101] U Control voltage [0102] U.sub.1 . . . U.sub.n
Control voltage [0103] S.sub.1 . . . S.sub.n Switch [0104] S
Selector switch [0105] T1 Resonator bank [0106] T2 Trimming element
[0107] VE Amplifier element [0108] R Resistor for adjusting the
operating voltage of an amplifier element [0109] C.sub.1, C.sub.2
Capacitor [0110] C.sub.1', C.sub.2' Digitally controlled capacitor
bank [0111] C.sub.3 Separation capacitor [0112] 1 Resonance curve
(frequency response of the admittance) of the resonator bank with
the first resonator switched in [0113] 2 Resonance curve (frequency
response of the admittance) of the resonator bank with the second
resonator switched in [0114] 3 Resonance curve (frequency response
of the admittance) of the resonator bank with the third resonator
switched in [0115] AN1, AN2 Matching network [0116] OUT Output
[0117] RF1, RF2 Terminals of the resonator [0118] PS, PS1, PS2
Piezoelectric layer [0119] PS', PS'' Additional piezoelectric layer
[0120] ES1 First electrode [0121] ES2 Second electrode [0122] GDE
(First) control electrode [0123] ME Metal layer [0124] SU Carrier
substrate [0125] AS Acoustic mirror [0126] W1 First transducer
[0127] W2 Second transducer
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